1. Field of the Invention
The present invention relates to a de-interlacing of an image sequence, and more particularly, to a motion-adaptive interpolation apparatus and method for accurately performing a de-interlacing.
2. Description of the Related Art
In general, an interlaced scan method has an advantage that a resolution in a vertical direction can be doubled even without raising a refresh rate of a screen, so that the resolution can be effectively improved with a limited frequency band.
However, the interlaced scan method has a disadvantage that it causes a screen jitter or a line crawl phenomenon that the screen moves up and down slowly.
Especially, in a still picture without a motion, the trembling of screen is very unpleasant to a user. A progressive scan method has been introduced to solves this problem.
For example, the NTSC interlaced scan method is performed by scanning an electron beam 60 times a second over the entire screen having 525 lines, whereby the electron beam is scanned 30 times to create 262.5 even lines, and remaining 30 times to create 262.5 odd lines. Accordingly, in terms of fields, 60 fields are reproduced in 1 second, while in terms of frames, 30 frames are reproduced in 1 second. On the other hand, the progressive scan method reproduces 60 frames in a second by scanning 525 scan lines at once.
A technique for converting an image sequence of an interlaced scan method to an image sequence of a progressive scan method is called a de-interlacing technique.
Conventional de-interlacing techniques are disclosed in U.S. Pat. No. 4,876,596 (Film-to-video converter with scan line doubling: Faroudja), U.S. Pat. No. 5,550,592 (Film mode progressive scan conversion; Markandey et al.), U.S. Pat. No. 5,563,651 (Method and apparatus for identifying video fields produced by film sources employing 2—2 and 3-2 pull down sequences; Christopher et al.), U.S. Pat. No. 5,596,371 (Film-mode video line-doubler motion detectors; Pakhchyan et al.), U.S. Pat. No. 5,689,301 (Method and apparatus for identifying video fields produced by film sources; Christopher et al.). Interpolation methods of the above techniques can be summarized by five methods as follows.
A first method is to interpolate by repeatedly using line information of the current field itself.
A second method is an interfield interpolation method that a very previous field data is inserted as it is between the current field line data without performing a motion compensation.
A third method is an intrafield interpolation method for interpolating by using a linear line interpolation of the current field itself.
A fourth method is a motion compensation interpolation method for interpolating by searching a motion vector.
A fifth method is a motion-adaptive interpolation method for interpolating based upon a motion by estimating a motion amount.
The first to third interpolation methods can be implemented by a simple hardware, but its picture quality is degraded after interpolation.
Referring to the fourth interpolation method, a picture quality is improved after interpolation, but its hardware construction is considerably complicated.
Meanwhile, the fifth method is implemented with a comparatively simple hardware, and its picture quality is improved after interpolation.
However, even if the fifth interpolation method is adopted, in case that only the motion between frames is detected, a motion of an object moving instantly or an object moving at a certain speed is hardly detected. In addition, even in case that a motion between simple fields is detected; it causes an excessive motion detection. Because of such an excessive motion, a resolution of an image after interpolation is degraded and overall picture quality is also degraded.
Accordingly, in order to more accurately detect a motion of an object, a plurality of memory units or a complicated processing procedure is required. It is inevitable that a complicated structure of the overall hardware is required and a manufacturing expense of a circuit for the construction is increased.